Crown Ether Complexes Of Potassium Research Articles

Strong dependence of air stability on thickness in n-doped carbon nanotube thermoelectrics

We demonstrate that the observed (in-)stability of n-doped carbon nanotube films in air not only depends on the employed dopant but is also strongly affected by sample-specific factors, such as the film thickness and density. We show this for two typical dopants, polyethylenimine and a potassium crown ether complex, by preparing films of increasing thickness. We argue that reports on dopant stability cannot be properly assessed without knowledge of these sample-specific parameters, which explains some of the conflicting results in the literature.

Crown ether complexes as a possible template for hybrid organic–inorganic borates

Abstract Crystals of the first new organo–inorganic hybrid borate based on potassium crown ether complex, [K(C12H24O6)B5O6(OH)4](H2O) (1), have been produced from aqueous solutions and characterized by single-crystal X-ray diffraction. 1 crystalizes is orthorhombic system, Pnma, a = 10.1684(3) Å, b = 11.6289(3) Å, c = 21.2247(6) Å, V = 2509.76(12) Å3, R obs = 0.059. The structure of 1 consists of molecular [K(C12H24O6)B5O6(OH)4]0 complexes, common for crown ether complexes but yet not among borates, with a very rare monodentate coordination of the common pentaborate anion(1-). The molecular complexes are linked into weak chains via hydrogen bonding to outer-sphere water molecules. Hirshfeld surfaces analysis and complexity measurement of 1 were performed. Perspectives of borate structures containing crown ether complexes as templates are briefly outlined.

Crown ether containing polyelectrolyte multilayer membranes for lithium recovery

Achieving solute selectivity has always been a goal of membrane development studies. The continuing growth of global consumption of scarce metals by different industries has put a strain on traditional sources of these species. Achieving cation selectivity in membranes, especially among monovalent cations, is a major step in introducing alternative sources for scarce metals such as lithium.Polyelectrolyte multilayer membranes (PEMMs) are a novel class of membranes, offering great potentials in monovalent/bivalent ion selectivity. On the other hand, crown ethers are a well-studied family of macrocyclic ligands capable of forming stable complexes with cations. In the current study, for the first time, we report on a PEMM nanofiltration membrane with crown ether moieties embedded in its structure for the goal of achieving monovalent salt selectivity. The crown ether 15-crown-5 was successfully incorporated in the polycation polyethylenimine (PEI), which was then used as the polycation in PEMM formation through layer by layer deposition. Both the synthesized polymer and the polyelectrolyte multilayer (PEM) were characterized and the performance of the resulting membrane was studied. It was determined that crown ether containing polymer forms more stable complexes with lithium than potassium. This was explained by the limitation put on 2:1 potassium-crownether complexes by steric hindrance from polymer chain. The manufactured membranes showed Li/K selectivity for a period of around 90 min, after which the crown ethers became saturated and selectivity was lost. The modified membranes became non selective after this point, but possessed high salt rejection potential.

Sequential X-ray-Induced Single-Crystal to Single-Crystal Transformation followed by Topotactic Reduction in a Potassium Crown Ether Complex of Tetrachloroaurate(III).

During data collection, the unreported potassium crown ether salt [K(18-crown-6][AuCl4] undergoes a sequential X-ray-induced and irreversible single-crystal to single-crystal transformation from P1̅ to C2/ c followed by a topotactic reduction to crystalline [K(18-crown-6][AuCl2] within the same C2/ c space group.

Comparison of two low flow interfaces for measurement of mobilities and stability constants by affinity capillary electrophoresis–mass spectrometry

Affinity capillary electrophoresis (ACE) is typically used for the determination of stability constant, Kst, of weak to moderately strong complexes. Sensitive detection such as mass spectrometry (MS) is required for extension of ACE methodology for estimation of Kst of stronger complexes. Consequently, an efficient interface for hyphenation of CE with MS detection is necessary. For evaluation of interfaces for electrospray ionization mass spectrometric (ESI/MS) detection in ACE conditions, potassium-crown ether complexation was used as model system. The effective mobilities of the crown ether ligands and the Kst of their potassium complexes were measured/determined by ACE-ESI/MS using two lab-made interfaces: (i) a sheathless porous tip CE-ESI/MS interface and (ii) a nano-sheath liquid flow CE-ESI/MS interface, and, in turn, compared with those obtained by ACE with UV spectrophotometric detection. Apparent stability constant of potassium-crown ether complexes in 60/40 (v/v) methanol/water mixed solvent, pH* 5.5, was about 1300 L/mol for dibenzo-18-crown-6, 1600 L/mol for benzo-18-crown-6 and 5200 L/mol for 18-crown-6 ligands, respectively. It was observed that electrophoretic mobilities from CE-MS experiments differ from reference values determined by UV detection by ∼7% depending on the CE-MS interface used. Good agreement of CE-MS and CE-UV data was achieved for nano-sheath liquid flow interface, in which the spray potential and the CE separation potential can be effectively decoupled. As for sheathless porous tip interface, a correction procedure involving a mobility marker has been proposed. It provides typically only ca. 1% difference of effective mobilities and Kst values obtained from CE-MS data as compared to those received by the reference ACE-UV method.

Isoselective Polymerization of rac-Lactide Catalyzed by Ion-Paired Potassium Amidinate Complexes.

Three potassium crown ether complexes supported with bulky amidinate ligands were synthesized for the ring-opening polymerization (ROP) of rac-lactide. The side polymerization reaction initiated directly by ligand anion was suppressed well in the presence of alcohol as our design, and the synthesis of linear polylactide with a molecular weight as high as 117.7 kg/mol was successful together with an isoselectivity value of Pm = 0.88 at -70 °C. In this system, lactide can be deprotonated by amidinate anion to give lactide enolate, which can initiate the ROP of lactide as a side reaction in the absence of alcohol; however, this side reaction can also be suppressed well in the presence of alcohol by a decrease in temperature. An interesting anti-Arrhenius-like behavior in the polymerization was discovered, which can be attributed to the fact that the active catalyst can be converted to a less active lactide enolate potassium complex at a high temperature.

Crown ether complexes of potassium quinolin-8-olates: synthesis, characterization and catalysis toward the ring-opening polymerization of rac-lactide

Crown ether complexes of potassium quinolin-8-olates were synthesized and demonstrated to catalyze the stereoselective polymerization of rac-lactide.

First Direct In Situ EPR Spectroelectrochemical Evidence of the Superoxide Anion Radical

For the first time, the superoxide anion radical was formed by electrochemical reduction of oxygen and detected in situ by EPR spectroscopy without changing the temperature. The spin susceptibilities of solid superoxide solutions were measured between 280 and 4 K showing Curie behavior. The EPR results were explained in the frame of an ion association and support the formation of a loose ion pair between the superoxide anion radical and the potassium crown ether complex. An alternative explanation for the large EPR line width of the superoxide anion radical at higher temperatures is given.

Metalation of toluene and cumene with alkali metal-crown ether complexes

Metalation of toluene and isopropylbenzene with alkali metal-crown ether complexes led to the corresponding α-metalated alkylbenzenes. Treatment of the latter in succession with solid carbon dioxide, water, and hydrochloric acid gave carboxylic or dicarboxylic acids in 65–78% yield. Metalation of isopropylbenzene with sodium or potassium crown ether complexes above 90°C was accompanied by cleavage of the polyether ring with formation of organometallic compounds which then reacted with isopropylbenzene to produce 2-sodio(potassio)-2-phenylpropane and open-chain oligoether.

Controlled Super-Structures of Hydrogen Bonding Ni<SUP>II</SUP> Complexes Organizing One-Dimensional Double Cationic Arrays

Anionic tris-biimidazolato Ni(II) complexes ([Ni(Hbim)3]-), which represent a hydrogen-bonding molecular building blocks, are self-organized to form honeycomb-sheet super-structures connected with complementary intermolecular hydrogen bonds by cations in the crystal. The crystal formed by the stacking of the sheets has nano-channel structures having width of ca. 2 nm-scale width, which confines one-dimensional double columnar arrays of cationic molecules. Thus, relative large cations such as potassium crown-ether complexes and PPh4+ can generally cause [Ni(Hbim)3]- to assemble to a honeycomb-sheet formation forming these channel structures. However, smaller cations such as 4-phenylethyl pyridinuim and trimethyl ethynyl ammonium also lead to the same honeycomb-sheet network by forming the cationic ion-pairs containing an anion in the channels; this is a new finding that we present in this paper.

Separation of chromium(VI) and chromium(III) with crown ether by means of ion-pair extraction.

A new method for the separation of chromium (VI) and chromium (III) with dicyclohexyl 18-crown-6 (DC18C6) in 1,2-dichloroethane was developed by means of solvent extraction. In this process, CrVI as HCrO4- was extracted as an ion-pair complex with the potassium-crown ether complex cation in the organic phase within 1 min. The extracted species was ascertained to be [K(DC18C6)]+ · [HCrO4]-. When mixtures of CrVI and CrIII were extracted under the optimum condition, CrVI alone was extracted quantatively, whereas CrIII remained in the aqueous phase. After extraction, CrVI in the organic phase was quantatively back-extracted by a 0.1 M NH3 solution. Then, each of the concentrations of CrVI and CrIII could be determined by means of inductively coupled plasma atomic emission spectromrtry (ICP-AES). Cations, such as iron (III), zinc (II) and cadmium (II), interfered with this extraction. The present method was applied to recover CrVI trace in the presence of CrIII in real samples, and clarified to be applicable to CrVI determination in natural water samples.

Double Channel Structures Based on Hydrogen Bonding Networks of 2,2′-Biimidazolate Nickel(II) Complexes

Abstract The [Ni(Hbim)3][K-DCH(18-crown-6)] (K-DCH(18-crown-6) = potassium cis-syn-cis-dicyclohexano-18-crown-6; Hbim = mono-deprotonated 2,2′-biimidazolate] is synthesized and the crystal structure is characterized by X-ray crystal analysis. (Crystal data: monoclinic, C2/m, a = 19.077(3) Å, b = 29.074(3) Å, c = 9.769(3) Å, β = 110.39(2)°, V = 5078(1) Å3, Z = 4) The crystal structure is characterized as a double channel structure. The larger channels of the two are produced by stacking 2D-honeycomb sheets of [Ni(Hbim)3]− complexes and the inner small channels is built up by two potassium-crown ether complexes which occupy the cavity of the large outer channel.

ANIONIC FIVE-COORDINATED CYCLIC ORGANOFLUOROSILICATES VARYING IN RING SIZE FROM FIVE- TO SEVEN-MEMBERED

Abstract Synthesis of the potassium crown ether complexes (K, 18-c-6) 3 and 4 of the anionic five-coordinated spirocyclic fluorosilicates from the precursor fluorosilanes has provided additional members of this new class of silicon compounds. Silicates 3 and 4 are monofluoro catecholate derivatives [(CH2) n SiF(O2C6H4)]−, containing the five-membered tetramethylene (n = 4) and six-membered pentamethylene (n = 5) ring system, respectively. X-ray analyses of these fluorosilicates are reported along with that of the previously synthesized related monocyclic anionic fluorosilicates [BiPhSiF3][K, 18-c-6] (1) and [BiBzSiF3][K, 18-c-6] (2). The first structural characterization of a pentacoordinated silicon compound containing a seven-membered ring is provided by 2. The study also yields the first structure of a fluorosilicate containing a six-membered ring (4). The geometries are all trigonal bipyramids. Silicates 2–4 have carbon-containing rings positioned diequatorially, whereas the trifluorosilicate 1, with ...

Crown ether complexes of potassium and thallium(I) 2- and 4-nitrophenoxides

18-Crown-6 and dicyclohexano-18-crown-6 complexes of potassium 2- and 4-nitrophenoxide, and 18-crown-6 complexes of thallium(I) 2- and 4-nitrophenoxide have been synthesized. Solvent effects on the visible spectra of the nitrophenoxide anions are independent of the nature of the cation and the nature of the complexing agent. The 18-crown-6 complex of thallium(I) 2-nitrophenoxide is a 1:2 complex. All the other complexes are 1:1. X-ray crystallographic examination of the potassium dicyclohexano-18-crown-6 complexes showed the potassium ion is octacoordinated in the 2-nitrophenoxide and heptacoordinated in the 4-nitrophenoxide.

Solvent extraction of gold(III) by benzo-15-crown-5 and characterization of the crystalline extracted complex

Gold(III) can be extracted efficiently into 1,2-dichloroethane with benzo-15-crown-5 (B15C5) from an aqueous solution containing hydrochloric acid and potassium ion. It is found that a bulky ion pair is formed by association of a potassium—crown ether complex cation and complex anion AuCl 4 − in the organic phase. The effects of acidity, temperature and other metal ions on the extraction have been studied. The apparent extraction equilibrium constant K ex has been measured to be 2.7 x 10 7 at 15°C and the enthalpy change Δ H for the extraction process to be -28.4 kJ mol −1. The crystalline extracted complex was characterized by elemental analysis, IR and UV—vis spectra, and its composition is found to be K(B15C5) 2AuCl 4.

Nature of the strong basicity of superbases, unsolvated hydroxide ions?

The basicity of so-called superbases is ascribed to the presence of free, i.e., naked, hydroxide ions. Infrared spectroscopic studies of various KOH (and KOCH 3) crown ether dicyclohexyl-18-crown-6 and dibenzo-18-crown-6) and Sr(OH) 2 cryptand(222) solutions in polar (methanol, chloroform) and non-polar solvents (toluene, n-heptane) revealed that unsolvated OH − ions are not present in such strong basic solutions. Formation of potassium crown ether complexes shown by the i.r. bands at 1095–1102 and 990–995 cm −1 (dicyclohexyl-18-crown-6) is always accompanied (and only possible if) by that of methoxide ions (i.r. band at 1050–1060 cm −1). The presence of solvated OH − ions cannot be excluded.

Spectrophotometric determination of potassium in river water based on solvent extraction of the complex formed with a crown ether and an anionic azo dye using flow injection

Potassium in water was determined by a spectrophotometric method involving flow injection coupled with solvent extraction. An ion association complex formed between the potassium-crown ether complex ion and an azo dye anion was extracted into an organic solvent and the absorbance of the separated organic phase was measured. Picrate and four analogues of 4-(4-dialkylaminophenyl)azo-2,5-dichlorobenzenesulphonate were examined as counter anions and three analogues of 18-crown-6 were examined as the crown ether. The use of several solvents was investigated. The results showed that 4-(4-diethylaminophenyl)azo-2,5-dichlorobenzenesulphonate and benzo-18-crown-6 were the most suitable reagents, benzene-chlorobenzene (1 + 1 V/V) being used for solvent extraction. The carrier stream was distilled water and the reagent stream contained the dye anion, crown ether, EDTA (dilithium salt) and lithium hydroxide. The organic phase was separated with a PTFE porous membrane. The sampling rate was 20 per hour. The calibration graph was linear at concentrations below 1 × 10–4M using samples of 20 µl. The detection limit corresponding to a signal to noise ratio of 3 was 1 × 10–6M and the relative standard deviation was 0.4%. Potassium in river water was determined satisfactorily by the proposed method.

Heat capacity of potassium-crown ether complexes in aqueous solution. Manifestations and quantitative treatment of important relaxational heat capacity effects

Heat capacity of potassium-crown ether complexes in aqueous solution. Manifestations and quantitative treatment of important relaxational heat capacity effects

Analytical Applications of Crown Ether Extraction of Cobalt Thiocyanate Complex With Ammonium-Crown Ether Complex

Abstract The effects of the ammonium-crown ether or the potassium-crown ether complex on the extraction of anionic species were studied. The cobalt thiocyanate complex was extracted into 1,2-dichloroethane by the addition of a crown ether complex. By measuring the absorbance of the organic phase at 623 nm, cobalt was determined spectrophotometrically. A linear calibration curve was obtained up to 10−4 M of cobalt in the aqueous phase.